Study finds biomass power not carbon neutral

When it comes to using biomass as an energy source, burning wood for heat is significantly better from a greenhouse gas perspective than using it to make electricity, according to a Massachusetts study.

Forested regions around the world are pursuing biomass as a renewable energy source but a study finds that the carbon footprint from burning biomass can be worse for global warming than coal.

The Manomet Center for Conservation Sciences on Thursday published the findings of a six-month study to measure the greenhouse gas impacts of using biomass, which, in many cases, does not meet claims of being "carbon neutral" over short periods of time.

The report was commissioned by the Massachusetts Department of Energy Resources, which said it will revise its regulations in response. "We can begin the process of refining our renewable energy regulations to provide incentives only for biomass energy that truly reduces our greenhouse gas emissions and protects our forests," said Massachusetts Department of Energy Resources Commissioner Phil Giudice, in a statement.

Wood pellets.
Martin LaMonica/CNET

The study has implications beyond Massachusetts since biomass was projected to see rapid growth as countries create policies to favor development of biomass as a source of renewable power in coming years.

Biomass plant operators have argued that biomass facilities are carbon neutral because trees absorb carbon dioxide when they grow. Carbon emissions from burning biomass are indeed offset by plant growth, but the Manomet study found that the time frame is measured in the decades, which calls into question the role of biomass in meeting carbon reduction goals.

When burned, forest biomass emits more greenhouse gases per unit of energy than fossil fuels, which the report calls the "carbon debt" of biomass. Regrowth of forests will pay off that debt and begin to deliver a "carbon dividend," in the form of lower greenhouse gas emissions than would have occurred if fossil fuels were burned.

The carbon debt payoff for using biomass instead of coal to make electricity is 21 years and more than 90 years compared to making electricity from natural gas.

Using biomass to make heat, rather than electricity, has a better environmental profile. Burning forest biomass to heat a building, such as a school, generally pays off its carbon debt within 10 to 20 years. Combined heat and power plants, which make electricity and heat, typically have lower emissions per energy unit compared to power-only facilities.

The results have implications for how Massachusetts and other regions manage forests, which is related to the cost of biomass since higher prices would create a stronger incentive to increase fuel supplies.

Manomet offered recommendations on ways to protect the local landscape and soil while operating a wood products industry over the long term. Each of the options is designed to promote sustainable wood procurement, such as requiring facilities to buy biomass from forests with state-approved forest management plans.

"The sobering conclusion is that Massachusetts cannot produce very much new energy from forest resources while also protecting the health of our forests and reducing greenhouse gas emissions," Sue Reid, a staff attorney for the Conservation Law Foundation (CFL), said in a statement. "The study echoes CLF's longstanding position that there are 'right' and 'wrong' ways to use biomass for energy."

In response, biomass industry people said that the study does not paint a completely accurate picture of biomass-to-power facilities because it assumes that they don't use residue wood products, such as branches and trees left from logging. "The study is not representative on how we plan to operate," Matt Wolfe of Madera Energy, which is proposing a wood-burning plant in western Massachusetts, told the Boston Globe.

The Biomass Power Association called the study misleading because it focuses on using forests as a source of biomass energy, rather than woody wastes and byproducts.

The report, though, notes that at least in Massachusetts at least, there is not that much residue available. "Understanding the greenhouse gas impacts of woody biomass energy is extremely complex," said Thomas Walker, who led the study.

Massachusetts is scheduling hearings in July on potential changes to biomass policies.

Updated on June 12 at 3:23 p.m. PT with statement from Biomass Power Association.

About the author

Martin LaMonica is a senior writer covering green tech and cutting-edge technologies. He joined CNET in 2002 to cover enterprise IT and Web development and was previously executive editor of IT publication InfoWorld.
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